The disclosure of Japanese Patent Application No. 2000-306074 filed on Oct. 5, 2000, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates generally to rolling control apparatus and method of a motor vehicle, such as an automobile, and more particularly to rolling control apparatus and method that control rolling of the vehicle by controlling braking force applied to a wheel or wheels of the vehicle.
2. Description of Related Art
A known example of rolling control apparatus of a vehicle, such as an automobile, is disclosed in, for example, Japanese Laid-open Patent Publication No. 10-81215. The known rolling control apparatus is constructed such that braking force is applied to a wheel or wheels on the outside of a turn if a parameter representing a rolling state of the vehicle exceeds a threshold value set for the purpose of preventing an excessively large degree of rolling.
In the rolling control apparatus as described above, if the parameter representing the rolling state of the vehicle exceeds the threshold value, the braking force is automatically applied to the wheels on the outside of the turn, so that the vehicle is decelerated with the radius of the turn of the vehicle being increased. As a result, the centrifugal force applied to the vehicle is reduced, and the vehicle is prevented from being brought into an excessive rolling state.
In the known rolling control apparatus as described above, the braking force is merely applied to the wheels on the outside of the turn when the parameter representing the rolling state of the vehicle exceeds the threshold value, but the roll angle of the vehicle is not controlled to a predetermined or desired angle. Accordingly, the roll angle of the vehicle may differ or vary depending upon the running conditions of the vehicle even when rolling control, i.e., vehicle stability control to suppress rolling, is performed. Thus, the known rolling control apparatus is not able to optimally control the rolling state of the vehicle regardless of the running conditions of the vehicle.
It is therefore an object of the invention to provide a rolling control apparatus that sets a target roll angle of the vehicle to be used in rolling control (i.e., vehicle stability control to suppress rolling), and controls braking force applied to each wheel so that the roll angle of the vehicle becomes equal to the target roll angle, whereby the rolling state of the vehicle is optimally controlled irrespective of the running conditions of the vehicle. It is another object of the invention to provide such a rolling control method.
To accomplish the above and/or other object(s), the invention provides rolling control apparatus and method for controlling rolling of a vehicle by controlling braking force applied to at least one wheel of the vehicle. A controller of the rolling control apparatus sets a target roll angle of the vehicle based on a rolling state of the vehicle, calculates a total control quantity for achieving the target roll angle, based on a running condition of the vehicle, and controls the braking force applied to each of the at least one wheel of the vehicle, based on the total control quantity.
In the rolling control apparatus constructed according to the invention as described above, the target roll angle of the vehicle is set based on a rolling state of the vehicle, and the total control quantity for achieving the target roll angle is calculated based on the running conditions of the vehicle, so that the braking force applied to each wheel of the vehicle is controlled based on the total control quantity. Accordingly, the roll angle of the vehicle is controlled to the target roll angle regardless of the running conditions of the vehicle, and therefore the rolling state of the vehicle can be optimally controlled regardless of the running conditions of the vehicle.
In a first preferred embodiment of the invention, the controller calculates a first target yaw moment for achieving the target roll angle by feed-forward control, based on the running condition of the vehicle, and calculates the total control quantity based on at least the first target yaw moment. In this case, the roll angle of the vehicle is efficiently controlled to the target roll angle, as compared with the case where the total control quantity is derived only from a control quantity for achieving the target roll angle through feedback control, for example.
In a second preferred embodiment of the invention, the controller calculates the total control quantity, based on a first control quantity for achieving the target roll angle by feed-forward control, and a second control quantity for achieving the target roll angle by feedback control. Here, the first control quantity is calculated based on the running condition(s) of the vehicle, and the second control quantity is calculated based on a deviation of an actual roll angle of the vehicle from the target roll angle. With this arrangement, the roll angle of the vehicle can be more appropriately controlled to the target roll angle, as compared with the case where the total control quantity is derived only from the first control quantity or the second control quantity.
In the second preferred embodiment of the invention, the first control quantity may be a first target yaw moment while the second control quantity may be a second target yaw moment, and the controller may calculate a final target yaw moment as the total control quantity, based on at least the first target yaw moment and the second target yaw moment. With this arrangement, the roll angle of the vehicle is more appropriately controlled to the target roll angle, as compared with the case where the final target yaw moment is derived only from the first target yaw moment or the second target yaw moment, i.e., as compared with the case where either the first target yaw moment or the second target yaw moment is defined as the final target yaw moment as the total control quantity.
In general, three equations of motion (1), (2) and (3) as indicated below are established in view of the balances among the forces in the rolling direction, yawing direction and the lateral direction of the vehicle.                                           M            ⁡                          (                              Vxd                +                                  θ                  ⁢                                      xe2x80x83                                    ⁢                  ydVx                                            )                                -                      MHθ            ⁢                          xe2x80x83                        ⁢            rdd                          =                                            -                                                Kf                  +                  Kr                                Vx                                      ⁢            Vy                    -                                                    LfKf                -                LrKr                            Vx                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            y            ⁢                          xe2x80x83                        ⁢            d                    +                      Kf            ⁢                          xe2x80x83                        ⁢            δ            ⁢                          xe2x80x83                        ⁢            f                    +                      Kr            ⁢                          xe2x80x83                        ⁢            δ            ⁢                          xe2x80x83                        ⁢            r                                              (        1        )                                                      Iyθ            ⁢                          xe2x80x83                        ⁢            ydd                    -                      Iyrθ            ⁢                          xe2x80x83                        ⁢            rdd                          =                                            -                                                LfKf                  -                  LrKr                                Vx                                      ⁢            Vy                    -                                                                                          Lf                    2                                    ⁢                  Kf                                -                                                      Lr                    2                                    ⁢                  Kr                                            Vx                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            y            ⁢                          xe2x80x83                        ⁢            d                    +                      LfKf            ⁢                          xe2x80x83                        ⁢            δ            ⁢                          xe2x80x83                        ⁢            f                    -          LrKr          +          N                                    (        2        )            xe2x80x83(Ir+MH2) xcex8rddxe2x88x92Iyr xcex8yddxe2x88x92MH(Vxd+xcex8rdVx)=xe2x88x92Croll xcex8rdxe2x88x92Kroll xcex8rxe2x80x83xe2x80x83(3)
In the above equations (1), (2) and (3), xcex8y, xcex8yd, xcex8ydd represent yaw angle, yaw velocity (yaw rate), and yaw acceleration of the vehicle, respectively, xcex8r, xcex8rd, xcex8rdd represent roll angle, roll rate (roll velocity), and roll acceleration of the vehicle, respectively, Vx, Vy represent longitudinal velocity and lateral velocity of the vehicle, respectively, and Vxd represents longitudinal acceleration of the vehicle. Furthermore, xe2x80x9cNxe2x80x9d is yaw moment of the vehicle, xe2x80x9cMxe2x80x9d is sprung mass, xe2x80x9cHxe2x80x9d is vertical distance between the axis of rolling of the vehicle and the gravity of the load on the spring, xe2x80x9cgxe2x80x9d is gravitational acceleration (acceleration of free fall), xe2x80x9cIrxe2x80x9d and xe2x80x9cIyxe2x80x9d are roll moment of inertia and yaw moment of inertia on the spring, respectively, and xe2x80x9cIyrxe2x80x9d is product of inertia on the spring with respect to the axis of rolling and the axis of yawing. xe2x80x9cKfxe2x80x9d and xe2x80x9cKrxe2x80x9d are cornering powers of tires of front wheels and rear wheels, respectively, and xe2x80x9cCrollxe2x80x9d and xe2x80x9cKrollxe2x80x9d are damping coefficient and spring constant of a suspension as measured in the rolling direction, xe2x80x9cLfxe2x80x9d and xe2x80x9cLrxe2x80x9d are distance between the gravity of the load on the spring and the axis of the front wheels as measured in the longitudinal direction (i.e., running direction) of the vehicle and distance between the gravity of the load on the spring and the axis of the rear wheels as measured in the same direction, and xe2x80x9cxcex4fxe2x80x9d and xe2x80x9cxcex4rxe2x80x9d are steering angles of the front wheels and the rear wheels, respectively.
In each of the above-indicated equations (1), (2) and (3), it is assumed that the unsprung mass is zero, the axis of rolling extends in the horizontal direction, and the roll angle of the vehicle is very small. On these assumptions, the position of the gravity of the load on the spring and the moment of inertia during rolling of the vehicle is substantially the same as those during non-rolling, and the sprung mass acts uniformly on the left and right wheels.
If xe2x80x9cNtxe2x80x9d represents target yaw moment for making the roll angle xcex8r of the vehicle equal to a predetermined target roll angle xcex8rt during a normal turn of the vehicle, the target yaw moment Nt is obtained by substituting xcex8rt for xcex8r and substituting Nt for N in the above equations (1), (2) and (3), as expressed in the following equation (4).                     Nt        =                                            {                                                -                                                            Kroll                      ⁡                                              (                                                  LfKf                          -                          LrKr                                                )                                                                                    H                      ⁡                                              (                                                  Kf                          +                          Kr                                                )                                                                                            +                                                                            KrollKfKr                      ⁡                                              (                                                  Lf                          +                          Lr                                                )                                                              2                                                                              MH                      ⁡                                              (                                                  Kf                          +                          Kr                                                )                                                              ⁢                                          Vx                      2                                                                                  }                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            rt                    -                                                    KfKr                ⁡                                  (                                      Lf                    +                    Lr                                    )                                                            Kf                +                Kr                                      ⁢                          (                                                δ                  ⁢                                      xe2x80x83                                    ⁢                  f                                -                                  δ                  ⁢                                      xe2x80x83                                    ⁢                  r                                            )                                                          (        4        )            
It will be understood from the above equation (4) that once the longitudinal velocity Vx of the vehicle, the steering angle xcex4f of the front wheels, and the steering angle xcex4r of the rear wheels are known, the target yaw moment Nt for controlling the roll angle xcex8r to the target roll angle xcex8rt can be calculated through feed-forward control. In the case where the rear wheels of the vehicle do not receive steering forces, the steering angle xcex4r of the rear wheels is set to zero.
In the first preferred embodiment of the invention as described above, the controller may calculate the first target yaw moment according to the above-indicated equation (4).
In the second preferred embodiment of the invention as described above, the controller may calculate the first control quantity according to the above-indicated equation (4).